Several of the characters in the books have visited the Other Railway or used it to travel from place to place. Many of the Fat Controller's engines came from the Other Railway originally. There have been several visitors from the Other Railway.

Although the fictional North Western Railway or Fat Controller's Railway was part of the nationalised railway network it kept most of its operating independence from British Railways on the mainland. This is why it escaped the infamous Beeching Report in the 1960s.

The Big City Engine, Gordon and Duck were involved in an argument over the confusion between the mainline stations in London. Gordon the Big Engine boasted about going to London, and believed that London was restricted to Kings Cross (served by the London and North Eastern Railway). Duck the Great Western Engine thought that London was Paddington, as he had once worked there as a station pilot (Great Western Railway). The Big City Engine thought that London was Euston (London Midland and Scottish Railway). Unbeknownst to them, they were all correct, but they did not realize, due to being on their own isolated lines before coming to Sodor, that there were a number of stations in London, and that these were merely three of them. Gordon was disappointed to discover when he visited London that the station he visited was St. Pancras.

It should be noted that the locomotive is never named in his one appearance. The name "Foreign Engine" is derived from the fact that in the Railway Series, engines not from the Island of Sodor are described as "foreign". The name "Big City Engine" was applied by Learning Curve when they produced the character for their range of wooden toys.

Jinty & Pug

Jinty and Pug are black steam locomotives who work on the Other Railway. They (amongst other engines) came to help out when the eight main engines went to England (in Eight Famous Engines), and practiced their work whilst the engines were still there. Jinty and Pug are revealed to be Percy's friends, and Jinty helped Thomas when he crashed through some buffers. Not much is known about them, as neither of them spoke, or played important roles in the one story in which they were featured. Jinty works mainly (and sometimes) in the Mainland working with Sparky, Neville, Stevie and 16.

Jinty is based on an LMS Fowler Class 3F0-6-0T. Small tank engines, and this class in particular, were nicknamed "Jinties" by railwaymen. Pug is based on an L&YR Class 21 (aka LMS Fowler Class 0F) 0-4-0ST. Four-wheeled saddletanks were affectionately nicknamed "Pugs" (see L&YR Class 21 for another example).

Diesel

Diesel is the Railway Series' first real villain - a scheming, oily trickster with a foul temper who likes to cause trouble wherever he goes. He was supposed to help Duck with his shunting, but he spread such mean-spirited rumours about Duck and the other engines that caused the Fat Controller to send him away.

The Diesel/D4711

This diesel came to Sodor to help out whilst Stepney was on the railway. He did not make a good impression on his arrival, as he told the engines that they should be scrapped and replaced by diesels like him. He soon got his comeuppance when he accidentally sucked in a Railway Inspector’s bowler hat during a maintenance check. He left soon afterwards, saying goodbye to no-one.

D4711 is based on a Class 40 diesel locomotive. His number is entirely fictitious and does not correspond to the numbering sequences used for any class of diesel locomotive on British Railways. The television series used the number D261, which would have been correct for a Class 40.

He made his one and only appearance in Stepney the "Bluebell" Engine. In that story he was referred to as "Diesel", but the television series revised this to "the Diesel" to avoid confusion with an earlier character by that name (although he is still sometimes referred to as "Diesel").

D199/199 Diesel/Spamcan

He visited Sodor on a trial with D7101 (later known as "Bear", see below), and talked about taking over the railway. He and Bear argued, and the other engines took an instant dislike to D199. One afternoon Henry the Green Engine found D199 moaning near a signal box because he had engine trouble, and the signalman called him "Spamcan". Henry rescued both the engine and his train, and D199 was soon sent away in disgrace by the Fat Controller.

D199 is a 1Co-Co1 diesellocomotive based on the British Rail Class 46. The number D199 is fictional but would be correct for a Class 46 if another six had been built: they were numbered from D138 through to D193.

Bear/D7101

Bear was originally known as D7101.

As described in the books, D7101 first arrived on the Island of Sodor on a trial for the Fat Controller. He was accompanied by another diesel engine, D199, who talked about taking over the railway. Later in the same story, Bear suffered from a failed ejector and had to be rescued by Henry. He befriended his rescuer, and the Fat Controller decided to give him a second chance. Bear was given a new number (D3) and a new coat of paint, and D199 was sent away in disgrace.

Bear attracted his nickname because of the sound of his engine, which is loud and gives off a growling sound he can't help. Bear was one of the later additions to the Railway Series universe, arriving in 1967. He is based on the British Rail Class 35 "Hymek" B-Bdiesel-hydraulic locomotive, first built in 1961.

Bear mainly pulls passenger trains, and sometimes pulls the Express if Gordon is not able to do so. He wears the two-tone green livery and the NWR number D3 he would have carried when built; when he arrived he wore British Rail 'Rail Blue' livery and the number D7101.

Like D199, Bear's number, D7101, is fictional but plausible; the final Class 35 was numbered 'D7100'.

Old Stuck-Up

Old Stuck-Up is a blue diesel engine who once visited the Island of Sodor. He visited to help the other engines, but ended up calling them names like "Dirty Old Smokey Things", and causing trouble. In return, the steam engines gave him his unflattering nickname. In the end, as Henry put it, "Old Stuck-Up came unstuck" when he slipped on a patch of oil left by BoCo and Bear and crashed into the engine sheds. He was sent home soon after, never to disturb the steam engines again.

The "Works Diesel"

This unnamed character once rescued James after a breakdown, and almost single-handedly changed James' opinion on diesels. He is a friendly sort who lives at Crovan's Gate and performs odd jobs around the railway. It is suggested in James and the Diesel Engines that he is one of a number of new diesels on the railway.

"Works Diesel" is a reader-applied name; he is unnamed in the stories themselves.

Pip & Emma

Philippa (Pip) and Emma make up an InterCity 125 High-Speed Diesel in The Railway Series. They have had problems with their cooling system and came to the railway when Gordon was on a journey. They soon made friends with all the engines.